The life cycle cost reduction for capital equipment such as gas turbines is of great importance to end users such as the Navy, the shipping industries and power generation stations to name a few. Regular maintenance of gas turbine equipment by the operators is necessary to maximize performance and fuel efficiency however the associated increased maintenance costs offset the benefits of shorter maintenance intervals. Achieving the optimal maintenance plan, which minimizes the total operation and maintenance costs, depends on the availability of accurate performance degradation assessments from diagnostic and prognostic technologies.
These maintenance-timing decisions were historically founded on rigid schedules based upon hours of use or when the operator noticed a severe degradation in the performance or efficiency of the turbine. The maintenance-timing was determined from examining the various turbine components during normally scheduled maintenance or through mechanical failure and estimating whether the average turbine should be maintained in a shorter or longer interval to maximize efficiency and minimize maintenance costs. The shortfall of this method was that the maintenance schedule was based on the average condition of a fleet of given turbine types, where unnecessary maintenance was done on some turbines where needed maintenance was forgone on other turbines resulting in poor performance or worse, catastrophic failure and overall added costs. In some turbines, when an injector or injectors were sufficiently clogged, the combustion process is uncontrolled and can cause visible flash of flame in the exhaust. This is hard to determine without specific diagnostic equipment that has been historically a thermocouple. The problem is that once the degradation was significant enough for the operator to perform out of schedule maintenance excessive fuel was wasted or worse was that fouling of the fuel nozzle caused harm to the turbine because of the shortfalls of the prior art diagnostic equipment.
Specifically, fuel nozzle fouling, can cause “hot starts” where uncontrollable ignition results in flame propagation through the turbine and damage to hot section components which necessitates expensive repairs and removing the affected turbine from service.
The Allison 501 turbine engine is used frequently in the Navy for shipboard power generation. The fuel nozzles in the Allison 501 engine often become clogged with internal or external carbon deposits. Fouling typically affects the pilot injection port more severely than the main port. The pilot port is used during engine startup and idle when the fuel flow rate is too low for proper atomization by the main port. A pressure-driven flow divider directs the flow to the appropriate port for proper atomization of the fuel for operation.
The fuel spray pattern is adversely affected by clogging and can lead to flame position problems that burn hot section components, and increases potentially damaging “hot starts” or “no starts”. Clogged injectors can delay ignition (“light-off”) during engine start-up and cause a buildup of fuel in the combustor. When ignition finally occurs, the unusually rich fuel/air mixture can cause excessive gas temperatures, temperature gradients and pressure gradients that damage hot section components. The excess fuel often produces a flash of flame in the engine's exhaust as well that may be detected visually.